Shunt loaded line phase shifter

ABSTRACT

A Differential Phase Shifter for operating at a center operating frequency is disclosed which includes a transmission line and a pair of shorting stubs attached thereto spaced a quarter wavelength apart at the center operating frequency. Each of the stubs are shorted at a distance greater than a quarter of a wavelength at the center operating frequency from the transmission line. A diode susceptible of being turned on or off is located on each of the stubs at a point less than a quarter of a wavelength from the main transmission line. The disclosure explains how to select the impedance values for the transmission line and the two stubs, as well as the spacing of the shorts and the diodes.

United States Patent Hatkin 1111 3,872,409 Mar. 18, 1975 SHUNT LOADEDLINE PHASE SHIFTER,

[75] Inventor: Leonard Hatkin, Elberon, NJ.

[73] Assignee: The United States of America as represented by theSecretary of the Army, Washington, DC.

[22] Filed: Apr. 30, 1974 [2]] Appl. No.: 465,450

Primary Examiner-James W. Lawrence Assistant Examiner-Marvin NussbaumAttorney, Agent, or Firm-Nathan Edelberg; Robert P. Gibson; Jeremiah G.Murray thereto spaced a quarter wavelength apart at the cen- [52] US.Cl. 333/31 R, 333/7 R, 3 3333/;/;)3, n ter Operating frequency Each ofthe Stubs are shorted [51] Int Cl H01 1/18 H03h 7/18 at a distancegreater than a quarter of a wavelength at [58] Fie'id 3 R A 33 97 thecenter operating frequency from the transmission 333/7 ,7 line. A diodesusceptible of being turned on or off is located on each of the stubs ata point less than a quarter of a wavelength from the main transmission[56] References cued line. The disclosure explains how to select theimped- UNITED STATES PATENTS ance values for the transmission line andthe two 3,434,906 7/1969 aytltin et al. I}; stubs, as well as thespacing of the shorts and the di. 3,4 1,314 1 1970 ite d 3.750.0557/1973 Funck 333/31 R 0 e i 10 Claims, 1 Drawing Figure 29 5015 .9? 5NETWUEW N i 16 l/ 11 Q7 1 e //l 34 7? 2/ cameo; s/a/v/u //v fg 5 t 4.

SHUNT LOADED LINE PHASE SHIFTER FIELD OF THE INVENTION This inventionrelates to a differential phase shifter and, particularly, to a shuntloaded differential phase shifter.

BACKGROUND OF THE INVENTION Numerous applications exist in whichcircuitry is required for differentially phase shifting a signal inresponse to a control signal. One particular use for a differentialphase shifter is in phased array radars.

In the March, 1965 edition of IEEE Transactions on MTT, Vol. MTT-l3, No.2, an article entitled High Power, p-i-n Diode Controlled, MicrowaveTransmission Phase Shifters by White, disclosed a differential phaseshifter in which a main transmission line has two shorting stubsattached thereto spaced from each other by 90 at a center operatingfrequency. In the White disclosure, a short is applied to each of thestubs at symmetrical points with respect to a point 90 from the maintransmission line at the center operating frequency. In each instance,the short closest to the main transmission line is' selectivelyremovable.

The White phase shifter is quite inexpensive to build and serves quitewell for small differential phase shifts. As the phase shift desiredincreases, the input admittance of the main transmission line begins totake on a large imaginary component mismatching the differential phaseshifter from the driving source. Furthermore, as the phase statechanges, that is, as the short is applied to either of the pointssymmetrical about a point 90 from the main transmission line, the signof this imaginary component changes, making it impossible to match theinput admittance for both phase states. It has been found that even forsmall differential phase shifts a small imaginary component is presentin the input admittance of the main transmission line.

Therefore, it is an object of this invention to provide a new andimproved differential phase shifter.

It is further object of this invention to provide a new and improveddifferential phase shifter which has areal input admittance which isindependent of the phase state.

It is a further object of this invention toprovide a known improveddifferential phase shifter with a configuration which can providedifferential phase shifts of substantial angles without introducingimaginary terms into the input admittance thereof. 1

BRIEF DESCRIPTION OF THE INVENTION With these and other objects in view,the present invention contemplates a differential phase shifter having acenter operating frequency and including a main transmission line havinga characteristic admittance of Y first and second shunt transmissionline stubs having characteristic admittances of Y,, and Y respectively,each of the shunt transmission line stubs have first ends thereofconnected to the main transmission line at locations spaced 90 from eachother. Each of the shunt transmission lines are provided with a devicefor selectively shorting the same at a location spaced from therespective first end thereof by a distance of 0, and 0 respectively, atthe center operating frequency, while a short is supplied on each of theshunt transmission line stubs at a location spaced from the respectivefirst ends thereof by a distance of (0, 24),) and (6 operatingfrequency; .and the following relationship is satisfied:

In the preferred embodiment, the device for selectively shorting thefirst and second shunt transmission line stubs include a diode and abias network responsive to control signal for passing current throughthe diodes.

DESCRIPTION OF THE DRAWING For a more complete understanding of theinvention, reference should be made to the following detaileddescription and drawing in which the sole FIGURE shows in schematic forma differential phase shifter embodymg the principles of this invention.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the sole FIGURE,there is seen a differential phase shifter 10 for operation at apredetermined center operating frequency which includes a maintransmission line 11, having a characteristic admittance of Y terminatedwith a resistor 12 having an admittance of Y A first shunt transmissionline stub 13 which has a characteristic admittance of Y, has a first end14 connected to the main transmission line II. A diode 16 has itscathode connected to the first shunt transmissionline stub at a point 17spaced from the first end thereof 14 by a distance of 6, at the centeroperating frequency. A signal responsive bias network 18 is connected tothe diode 16 by leads '19 and 21 to selectively pass current through thediode 16 in response to a control signal applied on a lead 22.

The first shunt transmission line stub is shorted at a point 23 which islocated a distance (6, 2(1),) from the point 14 at the center operatingfrequency, where (0, (15,) is at-the center operating frequency.

A second shunt transmission line stub 24 which has a characteristicadmittance of Y has a first end thereof 26 connected to the maintransmission line 11 at a point located 90 from the first end of thefirst transmission line stub 13 at the center operating frequency. Adiode 27 has its cathode connected to the second transmission line stubat a point 28 which is spaced from the first end thereof 26 a distanceof 6 at the center operating frequency. A bias network 29 is connectedto the diode 27 by leads 31 and 32 to selectively pass current throughthe diode 27 in response to the control signal being applied to a lead33. The leads 22 and 23 are connected to each other and a control signalis applied thereto by a lead 34 so that the bias networks 18 and 29 areactuated together.

The second shunt transmission line stub is shorted at a point 36 whichis located a distance (0 2%) from the first end thereof 26 at the centeroperating frequency, where (0 d is 90 at the center of operatingfrequency.

In operation a signal is applied to the input 37 of the differentialphase shifter 10. With no control signal applied to the lead 34, thesignal appearing across the resistor 12 has a fixed phase. Applicationofa signal to the lead 34 causes the bias networks 18 and 29 to passcurrent through the diodes 16 and 27, shorting the first and secondshunt transmission line stubs 13 and 24 at the points 17 and 28, causinga fixed differential phase shift in the signal appearing across theresistor 12. In

accordance with this invention, the proper selection of t the impedancesY and Y and the distances 0, and results in a real input impedance atthe terminal 37 independent of phase state.

By forming an expression for the input admittance of the differentialphase shifter and setting the imaginary portion thereof equal to 0, ithas been found that the input admittance of the differential phaseshifter 10, will be real when:

Y COt 01/1 Y2 COt Y2 COt 0 /Y From the above expression it can be seenthat the admittance of the lines 13 and 24 and/or the location of thediodes l6 and 27, can be altered in fixed relationship and still obtaina real input admittance for the differential phase shifter 10. Inaccordance with design considerations the location of the diodes 16 and28 (and therefore the shorts 23 and 36) can be the same while theadmittances of the shunt transmission line stubs l3 and 24 can be set toprovide the real input admittance. On the other hand,if designconsiderations dictate, the admittances of the shunt transmission linestubs l3 and 24 can be held the same and the location of the diodes l6and 27 can be set to accomplish the same result. In some instances boththe admittances and diode locations can be adjusted to achieve the realinput admittance as long as the relationship set forth above is met.

The value of Y and 6 are determined by the total differential phaseshift required. This relationship is given by While this invention hasbeen described with respect to a particular embodiment thereof, numerousother embodiments will become obvious to those of ordinary skill in theart in light thereof.

What is claimed is:

l. A differential phase shifter having a center operating frequency andincluding:

a main transmission line having a characteristic admittance of Y a firstshunt transmission line stub having a characteristic admittance of Ysaid first shunt transmission line stub having a first end connected tosaid main transmission line at a predetermined location;

means for selectively shorting said first shunt transmission line stubat a location spaced from said first end thereof by a distance of 6, atsaid center operating frequency;

means for shorting said first shunt transmission line stab at a locationspaced from said first end thereof 4 by a distance of (6,+2 ;b where (Od-(1),) is at said center operating frequency;

a second shunt transmission line stub having a characteristic admittanceof Y said second shunt transmission line stub having a first endconnected to said main transmission line at a location spaced from saidpredetermined location by 90 at said center operating frequency;

means for selectively shorting said second shun transmission line stubat a location spaced from said first end thereof by a distance of 0 atsaid center operating frequency.

means for shorting said second shunt transmission line stub at alocation spaced from said first end thereof by a distance of 0 +2 where0 is 90 at said center operating frequency; and the followingrelationship is satisfied:

Y1 Cot 91/ Y0 2 Cot 2m [1 (Y; coast/Yum.

2. The differential phase shifter as defined in cl i 1 also including:

means for terminating said main transmission line in an admittance of Y3. The differential phase shifter as defined in claim 1 in which 6, 0

4. The differential phase shifter as defined in claim 1 in Y1 Y2.

5. The differential phase shifter as defined in claim 1 in which saidmeans for selectively shorting said first shunt transmission line stubincludes:

a first diode; and

a first bias network responsive to a control signal for passing currentthrough said first diode.

6. The differential phase shifter as defined in claim 5 in which saidmeans for selectively shorting said second shunt transmission line stubincludes:

a second diode; and

a second bias network responsive to said control signal for passingcurrent through said second diode.

7. The differential phase shifter as defined in claim 6 in which'0 0 8.The differential phase shifter as defined in claim 7 also including:

means for terminating said main transmission line in an admittance of Y9. The differential phase shifter as defined in claim 6 in which Y, Y

10. The differential phase shifter as defined in claim 9 also including:

means for terminating said main transmission line in an admittance of Y

1. A differential phase shifter having a center operating frequency andincluding: a main transmission line having a characteristic admittanceof Y0; a first shunt transmission line stub having a characteristicadmittance of Y1; said first shunt transmission line stub having a firstend connected to said main transmission line at a predeterminedlocation; means for selectively shorting said first shunt transmissionline stub at a location spaced from said first end thereof by a distanceof theta 1 at said center operating frequency; means for shorting saidfirst shunt transmission line stub at a location spaced from said firstend thereof by a distance of ( theta 1+ 2 phi 1) where ( theta 1+ phi 1)is 90* at said center operating frequency; a second shunt transmissionline stub having a characteristic admittance of Y2; said second shunttransmission line stub having a first end connected to said maintransmission line at a location spaced from said predetermined locationby 90* at said center operating frequency; means for selectivelyshorting said second shunt transmission line stub at a location spacedfrom said first end thereof by a distance of theta 2 at said centeroperating frequency. means for shorting said second shunt transmissionline stub at a location spaced from said first end thereof by a distanceof ( theta 2+ 2 phi 2), where theta 2+ phi 2) is 90* at said centeroperating frequency; and the following relationship is satisfied: Y1 Cottheta 1/Y0 Y2 Cot theta 2/Y0 /( 1 + (Y22 Cot2 theta 2/Y02)).
 2. Thedifferential phase shifter as defined in claim 1 also including: meansfor terminating said main transmission line in an admittance of Y0. 3.The differential phase shifter as defined in claim 1 in which theta 1theta
 2. 4. The differential phase shifter as defined in claim 1 inwhich Y1 Y2.
 5. The differential phase shifter as defined in claim 1 inwhich said means for selectively shorting said first shunt transmissionline stub includes: a first diode; and a first bias network responsiveto a control signal for passing current through said first diode.
 6. Thedifferential phase shifter as defined in claim 5 in which said means forselectively shorting said second shunt transmission line stub includes:a second diode; and a second bias network responsive to said controlsignal for passing current through said second diode.
 7. Thedifferential phase shifter as defined in claim 6 in which theta 1 theta2.
 8. The differential phase shifter as defined in claim 7 alsoincluding: means for terminating said main transmission line in anadmittance of Y0.
 9. The differential phase shifter as defined in claim6 in which Y1 Y2.
 10. The differential phase shifter as defined in claim9 also including: means for terminating said main transmission line inan admittance of Y0.